1. Field of the Invention
The present invention is directed to a warning device for an x-ray source, and in particular to a device which warns when an excessively elevated temperature of the coolant contained in the radiation source housing occurs.
2. Description of the Prior Art
An x-ray generator (also referred to as an x-ray radiator) normally includes X-ray tube enclosed in a housing filled with a coolant, e.g. oil, which is circulated with the housing. (in the following discussion, for simplicity, oil is employed as a general representative of a coolant.) In rotating anode tubes a certain potential for danger results from the fact that heat is generated during operation and is stored in the rotating anode, and this heat can only be dissipated by convection, because of the danger that if the tube envelope (which is generally made of glass) breaks, the anode, with a temperature of 1000 K, will come into contact with the oil, and the oil then evaporates on the anode explosively. Under certain conditions such as high oil temperature, the resultant gases can cause the housing of the x-ray generator source to burst. It is possible for the examination subject and the attendants to sustain injury due to hot oil and parts ejected as a result of the explosion. For this reason, an x-ray source is usually provided with a sensor which immediately interrupts the operation of the electron emitter and shuts off the x-ray generator if a certain oil temperature, or if a certain oil pressure, arise within the housing. This results in the disadvantage that a new endangerment of the patient arises in certain examination methods such as a cardiac catheter examination due to the sudden loss of image information.
The danger caused by the sudden loss of image information can be diminished by a timely alarm signal commencing before the shutoff of the system. Such a signal can also be used to limit the operation of the X-ray generator to a lower, safe level. In the prior art this signal is created, for example, by means of an addition in the load computer. The load computer calculates the heat content of the X-radiation source in addition to the heat content of the anode and emits an alarm signal to the attendant upon attainment of a critical heat content with the danger of a shutoff. From this point in time, only an orderly (sequenced) aborting of the examination may still be performed. The loss of image information is thereby to a large extent prevented. Another possibility for creating an alarm signal is to measure the coolant pressure or coolant temperature and to transfer the respective signal to the system, where an alarm signal is then set off. A disadvantage of both methods is that they are very expensive and are consequently used only to a small extent. A further problem is that these warning means are only provided in new x-ray generators, as opposed to a considerable number of currently installed x-ray generator which must operate without such warning means.
From U.S. Pat. No. 5,497,410 it is known to provide an x-ray source with a temperature detector which sets off a switching process when a permitted temperature is surpassed, interrupting the x-ray source's energy supply, for example. The measuring sensor can be located externally of the protective housing.
From German OS 39 27 240 an x-ray source is known with a means for scanning and recording operating parameters of the x-ray source. These means are included in the protective housing of the x-ray source.
From German PS 973 690 optical or acoustical warning devices are known in the context of x-ray diagnosis, for example.